Method for surface stabilizing metal components

ABSTRACT

The invention relates to a method for the strengthening of the surface of a structural component with the aid of laser shock processing in which a coating applied to a metallic surface of the component to be strengthened is decomposed with the aid of a laser beam provided by a processing laser through evaporation or pyrolysis under creation of a plasma in such a way that a shock wave induced by interaction of the plasma with the metallic surface deforms the surface plastically and with the laser shock processing being monitored by means of recording light emission values of the plasma. In accordance with the invention, the light emission values are recorded with the aid of a measuring laser in time-delayed fashion relative to the decomposition of the coating with the aid of the processing laser.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase application submitted under 35 U.S.C. § 371 of Patent Cooperation Treaty application serial no. PCT/DE2008/000165, filed Jan. 31, 2008, and entitled METHOD FOR SURFACE STABILIZING METAL COMPONENTS, which application claims priority to German patent application serial no.: DE 10 2007 006 302.6 filed Feb. 8, 2007, and entitled VERFAHREN ZUR OBERFLÄCHENVERFESTIGUNG METALLISCHER BAUTEILE, the specifications of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The invention relates to a method for strengthening the surface of metallic structural components in accordance with the generic term of Claim 1.

BACKGROUND

From EP 1 637 616 A2, a method has been known for strengthening the surface of metallic structural components with the aid of laser shock processing. In laser shock processing, a coating is applied to the surface of a metallic structural component to be strengthened that is decomposed with the aid of a laser beam provided by a processing laser. The laser beam provided by the processing laser preferably involves a pulsed laser beam. With the aid of the pulsed laser beams, a plasma is generated from the decomposing coating, with shock waves being induced through the interaction of the plasma with the metallic surface of the structural component that deform the surface plastically, thereby inducing internal compressive stresses in the same. The surface of the structural component is thereby strengthened.

From EP 1 637 616 A2 it has furthermore been known to monitor the laser shock beam process by recording the light emission values of the plasma. Laser shock processing can be controlled or, respectively, regulated based on the measuring values recorded in this manner. According to EP 1 637 616 A2, the recording of the light emission values of the plasma occurs with the aid of a spectrometer, with spectral emissions of the plasma being focused via a lens and subsequently being fed into the spectrometer. A disadvantage of this recording of the light emission values of the plasma is the fact that the measuring values show a strong background signal of the plasma resulting from recombination radiation and bremsstrahlung (i.e., braking radiation) in the so-called plasma afterglow. Due to this strong background signal, it is virtually impossible to relate the recorded light emission values to the obtained surface strengthening with the effect that, based on the recorded light emission values, no conclusion can be arrived at with regard to the efficacy of the laser shock processing and that therefore only an imprecise regulation of the laser shock processing will be possible.

SUMMARY

Starting from the foregoing, the objective of the invention at hand is to create a new method for strengthening the surface of metallic structural components. This problem is solved by a method in accordance with Claim 1. In accordance with the invention, the light emission values of the plasma are recorded with the aid of a measuring laser in time-delayed fashion relative to the decomposition of the coating with the aid of the processing laser.

In accordance with the invention at hand, the light emission values of the plasma are recorded with the aid of a measuring laser in time-delayed fashion relative to the decomposition and thus to the creation of the plasma with the aid of the processing laser. This makes it possible to provide light emission values that are nearly free of any disturbing background signal of the plasma so that the recorded light emission values of the plasma can be correlated unambiguously to the laser shock processing. Therefore, on the basis of the light emission values recorded in accordance with the invention, a conclusion is possible with regard to the efficacy of a laser shock processing as well as precise control of the same.

Preferred further developments of the invention will result from the subclaims and the description set forth below.

DETAILED DESCRIPTION

The invention at hand relates to a method for the strengthening of the surface of metallic structural components with the aid of laser shock processing. The method finds preferred application in the strengthening of the surface of gas turbine components.

The basic principles of laser shock processing for the strengthening of the surface of metallic structural components are familiar to a person skilled in the art and do not require any detailed explanation. The basic principles of laser shock processing can be found, for example, in EP 1 637 616 A2.

In accordance with the invention at hand, the laser shock processing is monitored by means of recording light emission values of the plasma generated during laser shock processing, with the light emission values of the plasma being recorded with the aid of a measuring laser in time-delayed fashion relative to the generation of the plasma. The plasma is generated through the decomposition of a coating applied to the surface of the structural component to be strengthened with the aid of a processing laser.

Due to the time-delayed recording of the light emission values, the latter are almost free of any interfering background radiation of the plasma. Thus, the invention is based on the knowledge that background radiation resulting from recombination radiation and bremsstrahlung (i.e., braking radiation) in the plasma afterglow abates greatly immediately following the generation of the plasma. If therefore light emission values of the plasma are recorded in time-delayed fashion relative to the latter, they are almost free of any background radiation. In that case, it will then be possible to establish a correlation between the light emission values and the laser shock processing and to come to an unambiguous conclusion with regard to the efficacy of the laser shock processing.

Preferably, the time delay between the recording of the light emission values of the plasma and the generation of the latter amounts to a few nanoseconds, preferably between 5 and 50 nanoseconds. Preferably, the time delay between the recording of the light emission values of the plasma and the generation of the latter will lie within a magnitude of about 10 nanoseconds.

Preferably, a pulsed measuring laser is used as measuring laser, with a measuring pulse of the measuring laser being time-delayed relative to a processing pulse of a processing laser, preferably within the magnitude indicated above.

In accordance with an advantageous further development of the invention at hand, a carbon-containing varnish on an organic basis is applied as a coating to the surface of the structural component to be strengthened. This varnish on an organic basis is decomposed by means of pyrolisis with the aid of the processing laser in order to provide the plasma. Alternatively, it will also be possible to apply a metallic foil or, respectively, a metallic film, in particular an aluminum foil or an aluminum film, as coating to the metallic surface of the structural component. Such coatings are decomposed through vaporization with the aid of the processing laser. Subsequent to the pyrolisis or, respectively, to the vaporization, ionization occurs with electric excitation of coating-specific atoms or molecules, with this excitation being able to be recorded via the light emission values in measuring-engineering fashion because when carbon-containing varnish on an organic basis is decomposed through pyrolisis, C₂ molecules or also CH molecules or CH₂ molecules are excited in preferred fashion. If, on the other hand, an aluminum film or an aluminum foil is decomposed through vaporization, Al atoms or Al₂ molecules are excited in preferred fashion. In accordance with the invention, the light emissions of these specific atoms or, respectively, molecules are recorded in time-delayed fashion following the generation of the plasma with the aid of the measuring laser.

Based on the recorded light emission values, it will be possible to control a laser shock processing in an efficient manner. To this end, actual values of the light emission values are compared with pre-set desired values, with the parameters of the laser shock processing being able to be adapted on the basis of any deviations detected thereby. 

1-5. (canceled)
 6. A method for strengthening a metallic surface of a component, the method comprising the steps: applying a coating to a metallic surface of a component; decomposing the coating through one of evaporation and pyrolysis by means of a laser beam provided by a processing laser; forming a plasma from the decomposing coating; plastically deforming the metallic surface with a shock wave induced by interaction of the plasma and the metallic surface; recording the light emission values of the plasma with the aid of a measuring laser, the light emission values being recorded in time-delayed fashion relative to the decomposition of the coating by the processing laser; and whereby the surface strengthening of the metallic surface may be monitored.
 7. A method in accordance with claim 6, wherein the time delay between the decomposition of the coating and the recording of the light emission values is within the range from 5 nanoseconds to 50 nanoseconds.
 8. A method in accordance with claim 6, wherein: the processing laser is a pulsed laser that emits a processing pulse during the step of decomposing the coating; the measuring laser is a pulsed laser that emits a measuring pulse during the step of recording the light emission values; and the measuring pulse of the pulsed measuring laser occurs in time-delayed fashion relative to the processing pulse of the pulsed processing laser.
 9. A method in accordance with claim 8, wherein the time delay between the decomposition of the coating and the recording of the light emission values is within the range from 5 nanoseconds to 50 nanoseconds.
 10. A method in accordance with claim 9, wherein the time delay is about 10 nanoseconds.
 11. A method in accordance with claim 6, wherein the coating applied to the metallic surface comprises a carbon-containing varnish on an organic basis.
 12. A method in accordance with claim 11, wherein during the step of decomposing the coating, the carbon-containing varnish is decomposed through pyrolysis with the aid of the processing laser.
 13. A method in accordance with claim 6, wherein the coating applied to the metallic surface comprises one of a metallic film and a metallic foil.
 14. A method in accordance with claim 13, wherein the one of a metallic film and a metallic foil comprises one of an aluminum film and an aluminum foil.
 15. A method in accordance with claim 13, wherein during the step of decomposing the coating, the one of a metallic film and a metallic foil is decomposed through vaporization with the aid of the processing laser.
 16. A method for strengthening a surface of a component by laser shock processing, the method comprising: applying a coating to a metallic surface of the component to be strengthened; decomposing the coating with the aid of a laser beam provided by a processing laser; creating a plasma from the decomposing coating in such a way that a shock wave induced by interaction of the plasma with the metallic surface deforms the surface plastically; and monitoring the laser shock processing through the recording of light emission values of the plasma, the light emission values of the plasma being recorded by a measuring laser in time-delayed fashion relative to the decomposition of the coating by the processing laser.
 17. A method in accordance with claim 16, wherein the step of monitoring includes a measuring pulse of a pulsed measuring laser, which monitoring step occurs in time-delayed fashion relative to the step of decomposing, which decomposing step uses a processing pulse of a pulsed processing laser.
 18. A method in accordance with claim 17, wherein the time delay between the decomposition of the coating and the recording of the light emission values is within the range from 5 nanoseconds to 50 nanoseconds.
 19. A method in accordance with claim 16, wherein the coating is formed of a carbon-containing varnish on an organic basis, and this coating is decomposed through pyrolysis by the processing laser.
 20. A method in accordance with claim 16, wherein the coating is formed of one of a metallic film and a metallic foil, and this coating is decomposed through vaporization by the processing laser.
 21. A method in accordance with claim 20, wherein the coating is formed of one of an aluminum film and an aluminum foil.
 22. A method for strengthening the surface of metallic structural components, the method comprising the steps: applying a coating to a surface of a metallic structural component; decomposing the coating with a pulsed processing laser; ionizing the decomposing coating to form a plasma; plastically deforming the metallic surface with a shock wave induced by interaction of the plasma and the metallic surface; recording the light emission values of the plasma afterglow by a pulsed measuring laser after the background radiation resulting from recombination radiation and bremsstrahlung following the generation of the plasma has substantially abated.
 23. A method in accordance with claim 22, wherein the step of ionizing includes electric excitation of atoms and molecules specific to the coating.
 24. A method in accordance with claim 23, wherein the coating is a carbon-containing varnish on an organic basis, the coating is decomposed via pyrolisis, and the step of ionizing includes preferred excitation of one of C₂ molecules, CH molecules and CH₂ molecules.
 25. A method in accordance with claim 23, wherein the coating is one of an aluminum film and an aluminum foil, the coating is decomposed via vaporization, and the step of ionizing includes preferred excitation of one of Al atoms or Al₂ molecules. 